Challenge Library

Coding Challenges

5,893 curated questions across every arena — browse by topic, then jump into a live 3-minute battle to put them to the test.

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All types Multiple Choice Code Analysis Code

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All levels Beginner Intermediate Hard

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1,033 challenges matching your filters

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Multiple ChoiceHard
[System Design] Fallback Fail fast for failing services
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] Half-open test Fail fast for failing services
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] Benefits Fail fast for failing services
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] Command Separate read and write models
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] Query Separate read and write models
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] CQRS Separate read and write models
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] Materialized view Separate read and write models
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] Eventual consistency Separate read and write models
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] Key pattern Safe retries
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] Stripe pattern Safe retries
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] Idempotent HTTP Safe retries
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] Duplicate detection Safe retries
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] TTL on keys Safe retries
qasys-designsys-designqa
Multiple ChoiceIntermediate
[System Design] Round robin Distribute traffic
qasys-designsys-designqa
Multiple ChoiceIntermediate
[System Design] Least connections Distribute traffic
qasys-designsys-designqa
Multiple ChoiceIntermediate
[System Design] L4 vs L7 Distribute traffic
qasys-designsys-designqa
Multiple ChoiceIntermediate
[System Design] Health check Distribute traffic
qasys-designsys-designqa
Multiple ChoiceIntermediate
[System Design] Sticky sessions Distribute traffic
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] Producer/consumer Async decoupling
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] At-least-once Async decoupling
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] DLQ Async decoupling
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] Kafka vs RabbitMQ Async decoupling
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] Backpressure Async decoupling
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] Three pillars Monitor system health
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] Prometheus Monitor system health
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] Grafana Monitor system health
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] Distributed tracing Monitor system health
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] SLI/SLO/SLA Monitor system health
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] Shard key Horizontal partition
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] Range vs hash Horizontal partition
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] Rebalance Horizontal partition
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] Cross-shard joins Horizontal partition
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] Consistent hashing Horizontal partition
qasys-designsys-designqa
Multiple ChoiceIntermediate
[Testing] Line Code execution measurement
qatestingtestingqa
Multiple ChoiceIntermediate
[Testing] Branch Code execution measurement
qatestingtestingqa
Multiple ChoiceIntermediate
[Testing] Mutation Code execution measurement
qatestingtestingqa
Multiple ChoiceIntermediate
[Testing] 80% myth Code execution measurement
qatestingtestingqa
Multiple ChoiceIntermediate
[Testing] Threshold CI Code execution measurement
qatestingtestingqa
Multiple ChoiceHard
[Testing] Playwright Test full user flows
qatestingtestingqa
Multiple ChoiceHard
[Testing] Page Object Model Test full user flows
qatestingtestingqa
Multiple ChoiceHard
[Testing] Visual testing Test full user flows
qatestingtestingqa
Multiple ChoiceHard
[Testing] Flaky tests Test full user flows
qatestingtestingqa
Multiple ChoiceHard
[Testing] CI integration Test full user flows
qatestingtestingqa
Multiple ChoiceIntermediate
[Testing] Test database Test cross-component interaction
qatestingtestingqa
Multiple ChoiceIntermediate
[Testing] Testcontainers Test cross-component interaction
qatestingtestingqa
Multiple ChoiceIntermediate
[Testing] Contract testing Test cross-component interaction
qatestingtestingqa
Multiple ChoiceIntermediate
[Testing] Seed data Test cross-component interaction
qatestingtestingqa
Multiple ChoiceIntermediate
[Testing] Teardown Test cross-component interaction
qatestingtestingqa
Multiple ChoiceIntermediate
[Testing] Function mock Simulate dependencies
qatestingtestingqa
Multiple ChoiceIntermediate
[Testing] Module mock Simulate dependencies
qatestingtestingqa
Multiple ChoiceIntermediate
[Testing] Spy Simulate dependencies
qatestingtestingqa
Multiple ChoiceIntermediate
[Testing] Partial mock Simulate dependencies
qatestingtestingqa
Multiple ChoiceIntermediate
[Testing] Reset Simulate dependencies
qatestingtestingqa
Multiple ChoiceBeginner
[Testing] Jest Same test, multiple inputs
qatestingtestingqa
Multiple ChoiceBeginner
[Testing] Pytest Same test, multiple inputs
qatestingtestingqa
Multiple ChoiceBeginner
[Testing] DRY Same test, multiple inputs
qatestingtestingqa
Multiple ChoiceBeginner
[Testing] Table-driven Go Same test, multiple inputs
qatestingtestingqa
Multiple ChoiceBeginner
[Testing] Coverage boost Same test, multiple inputs
qatestingtestingqa
Multiple ChoiceIntermediate
[Testing] Jest Compare against stored output
qatestingtestingqa
Multiple ChoiceIntermediate
[Testing] Update flow Compare against stored output
qatestingtestingqa

Practice now, dominate the arena

Every challenge here is drawn from the live Code Royale pool. Review a question, then head to the arena to answer under pressure against a real opponent — 3-minute matches, Elo ranking, and badge tiers on the line.

Coding Challenges

[System Design] Fallback Fail fast for failing services

[System Design] Half-open test Fail fast for failing services

[System Design] Benefits Fail fast for failing services

[System Design] Command Separate read and write models

[System Design] Query Separate read and write models

[System Design] CQRS Separate read and write models

[System Design] Materialized view Separate read and write models

[System Design] Eventual consistency Separate read and write models

[System Design] Key pattern Safe retries

[System Design] Stripe pattern Safe retries

[System Design] Idempotent HTTP Safe retries

[System Design] Duplicate detection Safe retries

[System Design] TTL on keys Safe retries

[System Design] Round robin Distribute traffic

[System Design] Least connections Distribute traffic

[System Design] L4 vs L7 Distribute traffic

[System Design] Health check Distribute traffic

[System Design] Sticky sessions Distribute traffic

[System Design] Producer/consumer Async decoupling

[System Design] At-least-once Async decoupling

[System Design] DLQ Async decoupling

[System Design] Kafka vs RabbitMQ Async decoupling

[System Design] Backpressure Async decoupling

[System Design] Three pillars Monitor system health

[System Design] Prometheus Monitor system health

[System Design] Grafana Monitor system health

[System Design] Distributed tracing Monitor system health

[System Design] SLI/SLO/SLA Monitor system health

[System Design] Shard key Horizontal partition

[System Design] Range vs hash Horizontal partition

[System Design] Rebalance Horizontal partition

[System Design] Cross-shard joins Horizontal partition

[System Design] Consistent hashing Horizontal partition

[Testing] Line Code execution measurement

[Testing] Branch Code execution measurement

[Testing] Mutation Code execution measurement

[Testing] 80% myth Code execution measurement

[Testing] Threshold CI Code execution measurement

[Testing] Playwright Test full user flows

[Testing] Page Object Model Test full user flows

[Testing] Visual testing Test full user flows

[Testing] Flaky tests Test full user flows

[Testing] CI integration Test full user flows

[Testing] Test database Test cross-component interaction

[Testing] Testcontainers Test cross-component interaction

[Testing] Contract testing Test cross-component interaction

[Testing] Seed data Test cross-component interaction

[Testing] Teardown Test cross-component interaction

[Testing] Function mock Simulate dependencies

[Testing] Module mock Simulate dependencies

[Testing] Spy Simulate dependencies

[Testing] Partial mock Simulate dependencies

[Testing] Reset Simulate dependencies

[Testing] Jest Same test, multiple inputs

[Testing] Pytest Same test, multiple inputs

[Testing] DRY Same test, multiple inputs

[Testing] Table-driven Go Same test, multiple inputs

[Testing] Coverage boost Same test, multiple inputs

[Testing] Jest Compare against stored output

[Testing] Update flow Compare against stored output

Practice now, dominate the arena